Carbon nanotube coated capacitor electrodes

ABSTRACT

Devices and methods for their formation, including electronic devices containing capacitors, are described. In one embodiment, a device includes a substrate and a capacitor is formed on the substrate. The capacitor includes first and second electrodes and a capacitor dielectric between the first and second electrodes. At least one of the first and second electrodes includes a metal layer having carbon nanotubes coupled thereto. In one aspect of certain embodiments, the carbon nanotubes are at least partially coated with an electrically conductive material. In another aspect of certain embodiments, the substrate comprises an organic substrate and the capacitor dielectric comprises a polymer material. Other embodiments are described and claimed.

RELATED ART

One application of the use of capacitors in electronic devices is forde-coupling during power delivery to electronic components such ascentral processing units (CPU's). Such capacitors may be formed with anembedded structure, and should generally be formed to provide highcapacitance, while also being formed from materials that provide minimalthermal expansion mismatch problems with the underlying substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described by way of example, with reference to theaccompanying drawings, which are not drawn to scale, wherein:

FIG. 1 illustrates a micrograph of carbon nanotubes formed on asubstrate;

FIG. 2 illustrates a side view illustrating an electrode structureincluding carbon nanotubes extending outward from a metal surface, inaccordance with certain embodiments;

FIGS. 3(A)-3(D) illustrate certain processing operations for forming aplurality of capacitor regions on a substrate, in accordance withcertain embodiments; and

FIG. 4 illustrates an electronic system arrangement in which certainembodiments may find application.

DETAILED DESCRIPTION

Certain embodiments relate to capacitors formed for electronic devices,including embedded capacitors formed on a substrate. Embodiments includeboth devices and methods for forming electronic devices includingcapacitors.

Certain embodiments may find application as de-coupling capacitors usedin power deliver applications such as delivering power to a CPU. For thehigh capacitance desired in CPU de-coupling capacitors, ceramic thinfilm capacitors have been investigated. However, the use of ceramic thinfilm capacitors may be problematic due to thermal expansion mismatch,damage to the ceramic during etching and via formation processes, highprocessing temperatures required, and alignment accuracy when attachinga separately fabricated ceramic thin film capacitor to a substrate. Forexample, ceramic capacitors may have an undesirable thermal expansionmismatch with organic substrates.

FIG. 1 illustrates a photomicrograph of a multi wall carbon nanotube(MWCNT) array grown on a substrate. The carbon nanotubes have astructure that includes a relatively large surface area.

FIG. 2 illustrates a schematic side view of carbon nanotubes 4 formed ona metal layer 2, in accordance with certain embodiments. The carbonnanotubes 4 may include a electrically conducting layer 6, such as ametal, formed thereon, to increase the electrical conductivity of thecarbon nanotube surface. The carbon nanotubes 4 may be used as part of acapacitor electrode structure, for example, the structure illustrated inFIG. 3(D). The carbon nanotubes 4 grow outward from the substrate 2surface in a substantially perpendicular manner (including some that are90 degrees to the surface, some that are angled slightly from 90degrees, and/or some that are curved). The carbon nanotubes 4 provide asubstantially larger exposed surface area than a conventional capacitorelectrode surface. For instance, an electrode having carbon nanotubesmay in certain cases have a surface area some 400-30,000 times greaterthan a flat surface electrode capacitor. Carbon nanotubes may be grownusing a suitable method such as plasma-enhanced chemical vapordeposition (PECVD). Catalysts are generally used to assist in thenanotube growth, and it is believed that metals including, but notlimited to, nickel, iron, cobalt, molybdenum, and ruthenium, and theircompounds, are effective catalysts. As a result, such metals may beapplied to a substrate surface, for example, copper, using a suitableformation process such as, for example, a physical vapor deposition(PVD) process, and then the carbon nanotubes formed thereon.Alternatively, the carbon nanotubes may be formed directly onto metallicsubstrates or foils formed from such materials. The layer 6 may beformed on the nanotubes using any suitable formation process, forexample, a vapor deposition or a plating process. In certainembodiments, the layer 6 may be formed from a metal such as copper orgold.

Due to the large surface area of the carbon nanotubes 4, a largecapacitance may be obtained when using a relatively low dielectricconstant material as the capacitor dielectric. For instance, ceramicdielectric materials with high dielectric constants are often used forhigh capacitance capacitors. In certain embodiments, the use of thecarbon nanotubes permits high capacitance to be obtain when usingpolymer dielectric materials having a lower dielectric constant thanceramic dielectric materials. For example, due to the larger surfacearea of the electrode with carbon nanotubes coupled thereto, in certainembodiments, a polymer dielectric having a dielectric constant of 5 maybe used, whereas in a conventional ceramic thin film dielectriccapacitor, a ceramic material having a dielectric constant of 1000 maybe used. As a result, it is believed that in certain applications,embodiments of embedded capacitors having a polymer dielectric and oneor more carbon nanotube coated electrodes can be used as an alternativeto multi-layer ceramic chip (MLCC) capacitors.

FIGS. 3(A)-3(D) illustrate operations in a process for forming anelectronic device including embedded capacitors, in accordance withcertain embodiments. The capacitors include at least one capacitorelectrode having carbon nanotubes coupled thereto. A substrate 10includes a metal layer 12 formed thereon. The substrate 10 may incertain embodiments be a multilayer organic substrate. As illustrated inFIG. 3(A), the metal layer 12 may be patterned and etched to includeopenings therein to electrically isolate devices to be formed insubsequent operations. An interlayer dielectric layer 14 is formed onthe metal layer 12 and extends into the openings in the metal layer 12.

A lower capacitor electrode layer 16 is formed on the interlayerdielectric layer 14. The electrode layer 16 may be patterned and etchedto form openings therein, as illustrated in FIG. 3(B). A capacitordielectric layer 18 is then formed on the lower capacitor electrodelayer 16 and may extend into the openings of the lower capacitorelectrode layer 16. The upper capacitor electrode layer 20 is thenformed on the capacitor dielectric layer 18, as illustrated in FIG.3(C). The various layers may be laminated together using a suitablelamination method using pressure and heat.

The upper capacitor electrode layer 20 may then be patterned and etchedand/or laser drilled to form vias extending through multiple layers tocontact the metal layer 12 on the substrate 10. Electrical connectionmay be made from a metal region 22 formed on the capacitor electrodelayer 20, through the vias extending through upper capacitor layer 20,the capacitor dielectric layer 18, lower capacitor electrode layer 16,and the interlayer dielectric layer 14, to contact the metal layer 12.These operations may be controlled to form a device including twocapacitor regions 26 and 30, separated by a ground region 28, asillustrated in FIG. 3(D).

The capacitor electrode layers on which the carbon nanotubes are formedmay be formed from a variety of electrically conducting materials,including those described above as good catalyst materials for theformation of carbon nanotubes, including, but not limited to nickel,iron, cobalt, molybdenum, and ruthenium, as well as other metals such ascopper and copper alloys having a suitable catalyst formed thereon. Incertain embodiments, the electrode layers 16 and 20 may be formedseparately with the carbon nanotubes, and then positioned on thesubstrate as illustrated in FIGS. 3(A) and 3(C). Alternatively, forexample, a metal layer could be deposited onto the interlayer dielectriclayer, and then the carbon nanotubes grown onto the metal layer, to formthe electrode layer 16.

The capacitor dielectric may be formed from a variety of electricallyinsulating materials, including ceramics and polymers. To minimizethermal expansion mismatch when using an organic substrate, certainembodiments utilize polymer dielectric materials. One example of apolymer dielectric material which may be used is ABF (Ajinomoto Build-upFilm).

It should be appreciated that variations to the operations describedabove are possible. For example, the entire capacitor may be separatelyformed and then laminated as a unit to the substrate, instead of beingformed layer by layer. One or both electrodes may be formed to includethe carbon nanotubes, depending on various factors such as, for example,the desired capacitance. In alternative embodiments, certain operationsmay be performed in a different order, modified or removed. Moreover,operations may be added to the above described process and still conformto the described embodiments. For example, additional layers may beformed on top of the capacitor structures in the electronic device. Oneexample may include forming embedded capacitors with additional layersof electrodes and dielectric, to achieve higher capacitance. Otherexamples may form other types of electronic devices above or below theembedded capacitors. Embodiments may include a variety of differentstructural configurations than those illustrated in FIGS. 3(A)-3(D). Inaddition, as used herein, the term metal includes pure metals andalloys.

Assemblies as described in embodiments above may find application in avariety of electronic components. In certain embodiments, a device ordevices in accordance with the present description may be embodied in acomputer system including a video controller to render information todisplay on a monitor coupled to the computer. The computer system maycomprise one or more of a desktop, workstation, server, mainframe,laptop, handheld computer, handheld gaming device, handheldentertainment device (for example, a video player), PDA (personaldigital assistant), telephony device (wireless or wired), etc.Alternatively, a device or devices in accordance with the presentdescription may be embodied in a computing device that does not includea video controller, such as a switch, router, etc.

FIG. 4 schematically illustrates one example of an electronic systemenvironment in which aspects of described embodiments may be embodied.Other embodiments need not include all of the features specified in FIG.4, and may include alternative features not specified in FIG. 4. FIG. 4illustrates an embodiment of a device including a computer architecture200 which may utilize integrated circuit devices having a structureincluding capacitors formed in accordance with embodiments as describedabove. The architecture 200 may include a CPU 202, memory 204(including, for example, a volatile memory device), and storage 206(including, for example, a non-volatile storage device, such as magneticdisk drives, optical disk drives, etc.). The CPU 202 may be coupled to aprinted circuit board 207, which in this embodiment, may be amotherboard. The CPU 202 is an example of a device that may havecapacitors formed in accordance with the embodiments described above andillustrated, for example in FIG. 3(D). A variety of other systemcomponents, including, but not limited to input/output devices,controllers, memory and other components, may also include structuresformed in accordance with the embodiments described above. The systemcomponents may be formed on the motherboard, or may be disposed on othercards such as daughter cards or expansion cards.

The storage 206 may comprise an internal storage device or an attachedor network accessible storage. Programs in the storage 206 may be loadedinto the memory 204 and executed by the CPU 202 in a manner known in theart. The architecture may further include a network controller 208 toenable communication with a network, such as an Ethernet, a FibreChannel Arbitrated Loop, etc. Further, the architecture may, in certainembodiments, also include a video controller 209, to render informationon a display monitor, where the video controller may be embodied on avideo card or integrated on integrated circuit components mounted on themotherboard, for example. Other controllers may also be present tocontrol other devices.

An input device 210 may be used to provide input to the CPU 202, and mayinclude, for example, a keyboard, mouse, pen-stylus, microphone, touchsensitive display screen, or any other suitable activation or inputmechanism. An output device 212 including, for example, a monitor,printer, speaker, etc., capable of rendering information transmittedfrom the CPU 202 or other component, may also be present.

While certain exemplary embodiments have been described above and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative and not restrictive, and thatembodiments are not restricted to the specific constructions andarrangements shown and described since modifications may occur to thosehaving ordinary skill in the art.

1. A device comprising: a substrate; a capacitor formed on thesubstrate, the capacitor comprising first and second electrodes and acapacitor dielectric between the first and second electrodes; wherein atleast one of the first and second electrodes comprises a metal layer andcarbon nanotubes coupled thereto; and wherein a plurality of the carbonnanotubes are in contact with the capacitor dielectric.
 2. The device ofclaim 1, wherein at least a portion of the plurality of carbon nanotubesare at least partially coated with a metal.
 3. The device of claim 2,wherein the first and second electrodes each comprise at least one metalselected from the group consisting of nickel, iron, cobalt, molybdenum,and ruthenium.
 4. The device of claim 2, wherein the carbon nanotubesextend in a direction that is substantially perpendicular to theelectrode that the carbon nanotubes are coupled thereto.
 5. The deviceof claim 2, wherein the first electrode and the second electrode bothinclude a plurality of carbon nanotubes coupled thereto.
 6. The deviceof claim 2, further comprising a metal layer on the substrate and aninterlayer dielectric layer on the metal layer, wherein the firstelectrode is positioned on the interlayer dielectric layer, and whereinthe first electrode is positioned between the interlayer dielectriclayer and the capacitor dielectric layer.
 7. The device of claim 2,wherein the substrate comprises an organic material, and the capacitordielectric comprises a polymer.
 8. The device of claim 2, wherein thedevice comprises a computer system including: a central processing unitwhich includes the capacitor formed on the substrate; a memoryelectronically coupled to the central processing unit; an input deviceelectronically coupled to the central processing unit; an output deviceelectronically coupled to the central processing unit; and a videocontroller electronically coupled to the central processing unit.
 9. Amethod for forming a capacitor, comprising: positioning a firstelectrode layer on a substrate; positioning a capacitor dielectric layeron the first electrode layer; and positioning a second electrode layeron the capacitor dielectric layer; wherein at least one of the first andsecond electrode layers comprises a metal layer having carbon nanotubesextending therefrom, a plurality of the carbon nanotubes being incontact with the capacitor dielectric layer; and laminating the secondelectrode layer, the capacitor dielectric layer, and the first electrodelayer to the substrate.
 10. The method of claim 9, further comprisingproviding a metal coating on at least a portion of the plurality of thecarbon nanotubes.
 11. The method of claim 10, further comprising formingthe first and the second electrode layers to each comprise a metalhaving carbon nanotubes extending therefrom.
 12. The method of claim 10,wherein the substrate comprises an organic substrate, and the capacitordielectric layer comprises a polymer.
 13. The method of claim 12,wherein the metal comprises at least one metal selected from the groupconsisting of nickel, iron, cobalt, molybdenum, and ruthenium.
 14. Themethod of claim 10, further comprising forming an electricallyconducting layer and an interlayer dielectric layer between thesubstrate and the first electrode layer.
 15. The method of claim 10,further comprising: forming a plurality of vias through the secondelectrode layer, through the capacitor dielectric layer, and through thefirst electrode layer, to form a plurality of electrically isolatedcapacitor regions, and forming a plurality of electrical connectionsextending from the second electrode layer through the capacitordielectric layer, through the first electrode layer, through theinterlayer dielectric layer, and contacting the electrically conductinglayer, wherein the electrically conducting layer includes a plurality ofopenings which electrically isolate portions of the electricallyconducting layer from one another; and forming a ground region betweentwo of the electrically isolated capacitor regions on the substrate, theground region comprising an electrical connection electrically isolatedfrom the second electrode layer and extending through the secondelectrode layer, the dielectric layer, the first electrode layer, andthe interlayer dielectric layer, and contacting the electricallyconducting layer.